Head stud treatment

[tractorjames]

I used wards stainless studs and they seem very nicely made, and no problems. I coated the whole shanks of the studs and bolts with ceramic grease. I oiled the threads and then blew the oil off with the air line to leave a VERY thin film of oil on the threads because it makes me feel better and always have used this method. I always use the theory that if I am not sure why I want to do something the way I want to then do it exactly as the book (repair manual) says if that makes sense.

Studs and bolts all came out fine a year later (I know its probably not long enough for them to seize) and the ceramic grease was still the same as how it came out of the pot. It had not dried up like copper/normal grease seems to do.

James

[Bandit1200]

I'm not sure quite what you mean here. Did you drill out the old threads with the correct size drill, then use the supplied tap for the Helicoil? The installed Helicoil will be a tight fit on the new bolt until you have screwed it in and out again, in my experience, but it should feel fairly free once the Helicoil is bedded in, so to speak. I did all the threads in my heads and all the ones in the inlet tract (carbs, elbows, etc) and they exhibited that tightness to start with.

I can't quite work out what you mean by "using a same sized tap to open up the threads".

I used a 5/16 UNC second tap. Not the tap supplied with the helicoil kit.

Steve

[Motorsport Micky]

I used a 5/16 UNC second tap. Not the tap supplied with the helicoil kit.

Steve

And was the supplied tap a "bottom" tap ? If so there's your tightness unless the bolts are tight immediately.

Micky

[Bandit1200]

2016-10-22 16.15.23.jpg

And was the supplied tap a "bottom" tap ? If so there's your tightness unless the bolts are tight immediately.

Micky

Tried to attach photo of the tap but computer isn't playing today.
The tap is I think a plug tap but with a slight taper to start it.
The inserts, when in place appear too small from the beginning.
Hope you can make sense of this description.2016-10-22 16.15.23.jpg
This job is fighting me all the way!

With the helicoils inserted in the head that's off, after the 5/16unc tap is run down them, the bolts turn between 3 and 4 rotations before bottoming
Best wishes

Steve

[Motorsport Micky]

I'd pull the fitted coils ( use a scriber or pointed implement to pick out the helicoil end and pull out with pliers) and run the bottom or plug tap down the heads to clean out the last 4 or 5 thou from the threads, the helicoils should fit correctly then and the bolts will run down until they reach the end of thread.

Micky

[mole42]

I've never heard of putting a tap down the Helicoil, I'm pretty sure that's a no-no. You did break the tang off the coil? And retrieved it from the hole?

I'd go with what Micky says, pull the Helicoils, wind the supplied Helicoil size tap down the hole and insert new ones. Don't put a tap down the Helicoil!

Richard

[Bandit1200]

If I pick out the coils and rethread to install new coils what do I need to do to avoid same happening?
The threads are too small even to start the bolt.
I was most careful, even paranoid, to avoid drilling initial holes to avoid drilling into water jacket.
Yes, broke tangs off and retrieved with magnet.


Steve

[milothedog]

Not sure if I read this right? you need to use the tap supplied with the coil kit for the inserts. Not a the size you are trying to restore?

[Bandit1200]

Not sure if I read this right? you need to use the tap supplied with the coil kit for the inserts. Not a the size you are trying to restore?

I used the drill supplied with the kit then the tap supplied with the kit, then installed the inserts.
When I was not able to screw the IM bolts into the inserts I used a 5/16 unc tap to open them up on the head that's on the bench. This appears to have worked in that I can now screw the bolts in by 3 to 4 turns.

Steve

[milothedog]

I used the drill supplied with the kit then the tap supplied with the kit, then installed the inserts.
When I was not able to screw the IM bolts into the inserts I used a 5/16 unc tap to open them up on the head that's on the bench. This appears to have worked in that I can now screw the bolts in by 3 to 4 turns.

Steve

I would pick them out and start over. Can't say I have ever had this problem and have done countless over the years, the bolts should screw in by hand.

Without meaning to offend, if you use a cheap kit then you do get what you pay for. Expect to pay at least £25 for a decent (one size) kit.

Ian.

[marshman]

As Ian says never had the problem. Are you sure you definitely used the right size helicoil? Could you try one on a scrap piece of metal.

Here is a link to a post I made a couple of years ago when I "helicoiled" my heads.

http://socforum.com/forum/showthread.php?26031-Helicoiling-Heads&highlight=head+helicoil

Roger

[Bandit1200]

2016-10-22 23.15.23.jpgYes, I used the right sized helicoil and performed a test on the thermostat housing threads on a spare IM I have and that worked perfectly. I paid £29 for the kit with 10 inserts, photo attached

Thanks all for the advice on this frustrating issue.

I've just picked out the coils as advised by Mickey and Ian and will attempt to insert new coils.

I'm at Stoneleigh tomorrow and if you are there don't be surprised to be approached on the SOC stand by a desperate Stag owner asking for advice on alternator relocation, helicoils, EEWP and IM gasket sealing.

Thanks all for your help and patience.

Best wishes

Steve

[Bandit1200]

Having replaced the helicoils in both heads so the IM bolts can be screwed in by hand.
The initial problem was caused by my screwing the inserts too far in and I guess they reduced as they went in further.
I've loosely refitted the head using ceramic grease on the studs and bolts and bolted the IM into position with one bolt proving difficult.
I'm going down the pub now for dinner and a pint and approach the job tomorrow with a fresh mind.
Tomorrow it's head torque down following the advice earlier in this thread and reconnect the cam sprocket. I'm not looking forward to that particular task. Then its bolt on the alternator with the new bracket and refit exhaust downpipe and oil filter and other odd jobs before I can start installation of the EEWP.
I'm replacing various nuts, bolts and washers, observing the correct UNC/UNF threads but finding difficulty in finding the correct bolt lengths to match what's come out.

Please keep the advice and comments coming as I seem to be taking 1 step back for every 2 forward.

Best wishes

Steve

[jbuckl]

I had some original studs.... they were chromed. (wrong choice of finish for a head fastener)

Micky,
For clarity the change in friction between dry and lubricated joints is relatively small, what the bolt is coated with has a much greater effect. However lubricant does reduce the variability of clamping force. With dry materials the variation is 15% as I noted. I've back calculated the material strength based on 55lbft and get a proof stress of 600MPa which on a 7/16" UNC thread gives a preload of 33.5kN in a stud. This assumes that the design engineers used a 0.9 factor for preload over proof load. So with a 15% variance unlubricated studs will sit somewhere between 31kN and 36kN if that variation took place across the top line of studs then you could have the back of the head held down with 5kN less force than the front - in simple terms that's 0.5Te less. If this difference happens between the studs and bolts then it's no wonder heads warp.
You note that you don't know how much effect lubrication has. I tend to use the RoyMech tables for dry and lubricated joints which show the coefficient of friction drops by about 5 & 15% when lubricated so for dry steel to steel you would be looking at 0.12 dropping to 0.10 at worst assuming a constant surface profile so there is a known range and while you will increase the clamping force a you bring the variation down to about 9%. If you hold the torque constant at 55lbft then yes the clamping force will rise by 13% so use the lower torque value in 12.29.27 of 45lbft.
What is more interesting here is that I had a quick look at the tables for plated steel, I believe the original studs may have been galvanised giving a dry coefficient range of .14 to .23, changing to cadmium or phosphated drops this to .09 - 0.14, a far greater change than adding lubricant.

[LD334]

I got the galvanised point from the concours notes which say "Head bolts, studs...should be zinc plated." Mine are clearly not concours, they're iron oxide.